The rapid growth of Internet traffic implies in an ever-increasing demand for broadband access in FTTx architectures (where x could denote home, building, curb, etc). Passive optical networks (PON) are often the technology of choice for operators, thereby allowing reasonable operational and capital expenses.
Optical amplifiers, such as Erbium-doped fiber amplifiers (EDFA) and particularly semiconductor optical amplifiers (SOA), find many important applications in PON architectures, especially in architectures where reach extension (e.g. XGPON) is needed. In these so-called long-reach PONs, a midspan extender box is deployed somewhere between an optical termination line (OLT) and an optical distribution network (ODN), according to ITU-T Recommendation G.984.6. Moreover, SOAs can also be employed in centralized PON monitoring schemes for fault detection using optical time domain reflectometry (OTDR), either in central office (CO) for tunable OTDR (T-OTDR) implementation or in a remote node (RN), taking advantage of the presence of active elements inside the extender box. SOAs are particularly attractive for their high gain over a wide spectrum, low noise figure (NF), low polarization dependent loss (PDL) and fast response time. Moreover, they are usually small and need low power consumption in comparison to fiber amplifiers.
However, SOAs are usually limited to ˜13 dBm output power. This power limitation also places an upper bound on the maximum achievable dynamic range of the system.
Traditionally, the optical amplifier gain can be increased by increasing the so-called pumping rate, which corresponds to the rate of number of atoms that are excited from the lower to the higher energy level of the corresponding atomic transition. In the case of EDFAs, the pumping process is achieved by optical excitation, whereas in semiconductor devices such as SOAs the mechanism involves an electrical current. Therefore, in order to increase the SOA gain, the driving current is increased.
However, excess driving current can lead to an increase in the number of material defects of the device, both intrinsic and derived from manufacturing processes. It is a well-known fact that the gradual long-term degradation or wear-out of optoelectronic devices depends on the operating current density and temperature; moreover, current overstress can also increase the probability of catastrophic (sudden) partial or total damage of the device.